1. Field of the Invention
The present invention relates to an optical waveguide and an optical waveguide device. More particularly, it relates to an optical integrated circuit device used for an optical fiber communication system, an optical information processing system, an optical sensing system, an optical data registration system and the like, and in particular relates to those advantageously used as an optical switch and an optical modulator.
2. Description of the Related Art
Recently, a single mode optical fiber and a single wavelength laser have been progressed and as a result, a high speed optical data transmission of Gb/s has practically been utilized. In particular, the optical waveguide device, which is highly adapted for a single mode optical fiber, will in the future develop an optical fiber communication system.
To build up the optical fiber communication system, it is indispensable to use an optical device, such as an optical matrix switch, the optical modulator etc.
In an optical integrated circuit, such as optical matrix switch, optical modulator and the like, a Ti diffused LiNbO.sub.3 channel waveguide is generally utilized. This comes from the reason that, LiNbO.sub.3 has a relatively large electro-optic constant among other stable inorganic crystals and gives an advanced effect to the device using the electro-optic effect.
Hitherto, it has been well known that a Mach-Zehnder optical interferometer is constructed by using the optical waveguide, thereby producing the optical switch and the optical modulator, as reported in "IEEE, J.Quantum. Electron.", vol.QE-13, No.4, pp.290(1977) by T. R. RANGANATH et al.
However, for the Mach-Zehnder optical modulator proposed by NORMANDIN et al., as reported in "Appl. Phys. Lett.," vol.34, No. 3, pp.200(1979) by R. Normandin et al., and "J. Opt. Commun.," vol.9, No. 1 pp. 19(1988) by M. Rottschalk et al., (1) an LiNbO.sub.3 optical waveguide produced by a Ti diffusion method suffers large optical damage due to its Ti content and accordingly a waveguide for visible light is not available, (2) an LiNbO.sub.3 optical waveguide produced by a proton exchange method, after the waveguide has been formed, has a different crystalline characteristic from that of a virgin LiNbO.sub.3, and together with the other reason, an electro-optic constant is smaller than that of a bulk crystal. Accordingly, when such an optical waveguide is used as the optical device for an optical directional coupler and an optical modulator, etc., then a problem has arisen in an inability to realize the electric-power-saving and the minituarization because a larger switching voltage and a longer effective length are required.